Method and means of burning solid



6. AUTWHAUC TEMP ERAwm; 23 & HUWDH'Y REGULAUON.

Feb. 19, 1935. T. McDONALD ET AL METHOD AND MEANS OF BURNiNG SOLID FUELpril 6, 1932 [NI/P/YI'OR; 7 0/75; /79 000,020 Cur-F0120 AUWWAW, \t i H236 8!. hilt/WHY RtbULi-MON.

a Patented Feb. 19, 1935 1,991,691

UNITED STATES PATENT OFFICE 1,991,691 METHOD AND MEANS OF BURNING SOLIDFUEL Thomas McDonald and Clifford J. Paisley, Toronto, Ontario, Canada,assignors to Minneapolis-Honeywell Regulator Company, Minneapolis,Minn., a corporation of Delaware Application April 6, 1932, Serial No.603,550 18 Claims. (Cl. 236-9) The present invention relates toimprovements D -tll e f Combustion Will rise to e point indiin themethod and mechanism for burning solid cating that such a condition hasbeen reached fuel particularly under automatic control for doand that nomore fuel should be fed to the furmestic purposes. nace until thetemperature of combustion be- J In one of the well known types of priorart C meS lowered.

devices for automatically burning solid fuels it An object of he presenti v n i n, h r r has been usual to supply fuel and air sim lt is theprovision of a mechanism which will norneously and concurrently wheneverthe temperamally d l and air at e Sam t m w enture of the space to beheated became less than v the space o e hea ed falls bel w that tem- 10that desired. In such systems wherein the fuel p r re w ich it isdesired to maintain and t0 and air feeds are simultaneously started a ddiscontinue the feeding of fuel but continue the stopped, it oftenhappens that large quantities feeding of When the temperature ofCombusof unburned fuel are discharged into the ash pit t n es o a Pointindicating that the furnace resulting in a serious loss ineconomy inoperation. s been pp d With ha amount of fu This is due to the fact thatonly slow and deswhich it can economi ally and completely burn. ultoryburning of the fuel is present after the More specifically, we providetwo electric deair feed is stopped. When the air and fuel feedvices, oneof which controls the feed of fuel and ing means are again started alarge quantity of the other of which controls the feed of air to aunburned fuel is likely to be left in the fire-box furnace. These twoelectric devices are normally 10 which fuel in turn is displaced intothe ash pit u der the ntrol of a ther ta usually 1 upon the feeding offresh fuel. ferred to as the room thermostat so that they are In orderto overcome this difficulty it has been p at d Whenever the mo falls heW th deproposed to operate the fuel feed for a given sired temperature.A second thermostat which percentage of time that the air feed isoperated. is Subject to the temp of Combustion In this manner it hasbeen possible to prevent a terrllpts Operation of e electric deviceWhich certain amount of the discharge of unburned controls the feed offuel whenever the temperafuel from the fire-box into the ash pit butthis ture of combustion rises above a point indicative system of burningsolid fuel does not take mm of the condition wherein all of the fuelthat can account the varying rates at which the same fuel be handled bythe furnace has been supplied to may burn under different conditions ofoperait. The combustion thermostat, however, does tion. In an effort toovercome the condition t d s o feeding 0f While the leem where unburnedfuel is disposed in the ash it, it thermostat is still below the desiredtemperature. has been proposed to feed air constantly even A furtherobject of the invention is the proviwhen the space to be heated is abovethe desired sion of means for pr v in X iI lli hmeI Of temperature but,of course, it will readily be apthe fire under low heat requirementconditions 35 preciated that in such a system, while the disincombination with the devices above mencharge of unburned fuel might beprevented, on tioned. the other hand the fuel is, of course, beingFurther objects of the invention will become burned more rapidly thandesired during such apparent as the description thereof proceeds.

times as the space to be heated is at or above the For a further andmore complete understand- 40 desired temperature. ing of the inventionreference may be had to the The primary object of the present inventionfollowing description and accompanying drawis to provide a method andmechanism for burnmg, in which: ing solid fuel preferably underautomatic control Figure l is a diagrammatic view showing one fordomestic use in which the disposing of unmanner in which our inventionmay be carried burned fuel in the ash pit will be avoided so far out, asis practicable without burning the fuel at an And Figure 2 is asectional view with parts unduly high rate during periods when the spacebroken away of one type of combustion thermoto be heated is at or abovethe desired temperastat that may be utilized in the system of Figture.ure 1.

It has been found that the temperature of Referring to the drawing, athermostat adaptcombustion has a definite relation to the burned to beplaced in the space to be heated and ing capacity of the furnace andthat when the hereinafter referred to as the room thermostat furnace hasreceived all of the fuel that it can is generally indicated at 10. Theroom thermoadequately handle and completely burn the temstat comprises abimetallic element 11 secured at one of its ends as indicated at 12 andcarrying a contact at its other end as indicated at 13. Contact 13engages a cooperating contact 14 whenever the temperature to which theroom thermostat is subjected falls below a predetermined minimum.

A combustion thermostat generally indicated at 15 may comprise a casing16 to which is secured a laterally extending tubular member 1'7. Ahelically coiled bimetallic element 18 has one of its ends secured tothe outer end of tubular member 1'7. A torsion rod 19 which terminateswithin casing 16 extends through tubular member 1'7 and helicalbimetallic coil 18 and has its outer end bent to substantially a rightangle in respect to the axis of the torsion rod as shown at 20. The freeend of the part 20 of torsion rod 19 is secured to the outer free end ofbimetallic element 18 by such as the nuts 21. The end of torsion rod 19which extends into and terminates within casing 16 is provided withscrew threads as shown at 22. Torsion rod 19 supports a pair of arms 23and 24 which are adjustably secured thereto by means of pairs of nuts 25and 26 which are received on the screw threaded portion 22 thereof. Eachof the arms 23 and 24 is provided with a mercury switch holder 2'7 and28 which in turn support mercury switches 29 and 30. The mercuryswitches 29 and 30 are of usual construction and comprise sealedcontainers of suitable glass into which extend electrodes whichcooperate with a body of mercury for making and breaking contact betweenthe electrodes as the mercury switches are tipped or rocked. Ashereinbefore stated, the arms 23 and 24 are adjustably mounted ontorsion rod 19 and for use in this particular system the switch 29 willbe known as a low limit switch and is adjusted so as to close a circuitwhenever the combustion temperature falls below approximately F.Likewise the switch 30 will hereinafter be referred to as a high limitswitch and it is so adjusted that it opens a circuit whenever thetemperature of combustion rises above a predetermined maximumtemperature of about 500 F.

The combustion thermostat 15 may be placed in the stack of the furnaceor at any other point wherein it responds directly and quickly to thetemperature of the products of combustion or of the fire itself. It mayrespond only to the temof the products of combustion or to radiant heatfrom the fire or to any combination of them so long as the temperatureof the combustion thermostat quickly responds to the changes of thecondition of the fire and is subjected to a temperature which bears somedirect relation to the condition of the fire.

The fuel feed means and the air feed means are herein shown as electricmotors numbered 31 and 32 respectively which may operate theconventional screw feed and air blower. The system also includes a relayhaving a coil 33 which operates an armature 34 which in turn controls acontact arm 35 adapted to cooperate with a stationary contact 36. Therelay in this particular instance is of that type which moves contactarm 35 from engagement with contact 36 under the action of gravity whencoil 33 is de-energized and in which the armature 34 positively movescontact arm 35 into engagement with contact 36 when relay coil 33 isenergized.

Operation With the parts in the position shown the room or space to beheated is above the desired temperature and the temperature ofcombustion is above the minimum for which low limit switch 29 is set andbelow the maximum for which high limit switch 30 is set. The fuel andair feed motors 31 and 32 are not being operated and consequently thetemperature of the room is lowering. When the temperature of the roomhas lowered sufficiently, bimetallic element 11 will cause contact 13 toengage contact 14 setting up the following energizing circuit for relaycoil 33; hot line 3'7, wires 38, 39, bimetallic element 11, contact 13,contact 14, wire 40, relay coil 33, and wire 41 to ground line 42.Energization of relay coil 33 attracts armature 34 to move contact arm35 into engagement with contact 36. Such action energizes feed motor 31as follows: hot line 3'7, wire 43, contact 36, contact arm 35, wire 44,wire 45, high limit switch 30, wire 46, feed motor 31, wire 4'7, andwire 48 to ground line 42. Fan motor 32 is simultaneously energized bythe following circuit: hot line 3'7, wire 43, contact 36, contact arm35, wire 44, wire 49, fan motor 32, wire 50, and wire 48 to ground line42.

The temperature of combustion begins to rise as a result of operation ofthe fuel and air feed and when the temperature of combustion rises abovethe setting of high limit switch 30 the circuit to the fuel feed motor31 will be interrupted. Such action indicates that the furnace has beensupplied with as much fuel as it can completely burn. It will be notedthat the supply of air is not interrupted since the circuit of fan motor32 is not controlled by the high limit switch Heat is still generated bythe furnace since it has been provided with its full capacity of fueland air under forced draft is still being supplied. Should the fuelwhich has been supplied to the furnace become consumed to such an extentthat the temperature of combustion again lowers, high limit switch 30will re-establish a circuit through feed motor 31 and more fuel will befed until the combustion temperature again rises above the setting ofthe high limit switch 30 indicating that the condition wherein thefurnace has been supplied with all the fuel it can completely burn hasagain been reached. This intermittent operation of the fuel feed motor31 in accordance with the temperature of combustion will continue untilthe room has been restored to the temperature it is desired to maintainwhereupon bimetallic element 11 will separate contact 13 from contact 14completely shutting down the system.

In this system provision is also made for operating the fuel and airfeed sufficiently often to prevent a complete consumption of all thefuel in the furnace which would result in extinguishment of the fire. Inthis particular instance the fuel and air feed motors 31 and 32 areoperated every time the below the setting of low limit Of course, othermethods of preventing extinguishment of the fire under low heatrequirement conditions could be used if desired.

Assuming, however, that the temperature of combustion falls below thesetting of low limit switch 29 indicating that the fire will soon go outif additional fuel and air is not supplied, an energizing circuit forrelay coil 33 will be established as follows: hot line 3'7, wire lowlimit switch 29, wire 52, wire 40, relay coil 33, and wire 41 to groundline 42. Energization of relay coil 33 results in operation of feedmotor 31 and fan motor 32 as described heretofore. When the temperatureof combustion rises above 38, wire 51,

REGULAUON.

the setting of low limit switch 29 the circuit to relay coil 33 will beinterrupted and the feed motor 31 and fan motor 32 will be stopped.

From the foregoing description it will be evident that this inventionprovides an eflicient automatic method and means for burning solid fuelin which the fuel feed is operated intermittently according to thetemperature of combustion and in which the air feed is constantlyoperated whenever the space to be heated falls below the desiredtemperature. In combination with these features the invention alsoprovides means for preventing extinguishment of the fire under low heatrequirement conditions.

Although a specific embodiment of the invention has been herein shownand described it is to be understood that various changes andmodifications could be made and we are to be limited only in the purviewof the appended claims. While mercury switches have been shown in thecombustion thermostat 15 and open contacts have been shown in the roomthermostat 10, it is to be understood that either of these thermostatsmay be provided with any type of contacting mechanism desired and may bemodifled in construction so long as they perform the necessaryfunctions.

We claim:

1. A control system for an automatic stoker including an air feed and afuel feed comprising, in combination, a thermostatic device located inthe space to be heated, a furnace thermostat directly responsive to thetemperature of combustion, means under the control of the thermostaticdevice for operating the air feed and fuel feed when the temperature ofthe space to be heated is below that desired, and means under thecontrol of the furnace thermostat for preventing operation of the fuelfeed only when the temperature of combustion rises above a predeterminedmaximum.

2. A control system for an automatic stoker including van air feed and afuel feed comprising, in combination, a thermostatic device located inthe space to be heated, a furnace thermostat directly responsive to thetemperature of combustion, means under control of the thermostaticdevice for operating the air feed and fuel feed when the temperature ofthe space to be heated is below that desired, means under control of thefurnace thermostat for operating the air feed and fuel feed when thetemperature of com-- bustion falls below a predetermined minimum, andmeans under control of the furnace thermostat for preventing operationof the fuel feed only when the temperature of combustion rises above apredetermined maximum.

3. A control system for an automatic stoker including an air feed andfuel feed, comprising, in combination, a thermostatic device responsiveto the temperature of the space to be heated, a furnace thermostatdirectly responsive to the temperature of combustion, means undercontrol of the thermostatic device for operating the fuel feed and airfeed when the temperature in the space to be heated falls below apredetermined minimum, and means under the control of the furnacethermostat for stopping and starting the fuel feed as the temperature ofcombustion rises above and falls below a predetermined maximumtemperature during the time the thermostatic device is below the minimumtemperature.

4. A control system for an automatic stroker including an electricallyoperated fuel feed motor and an electrically opera ed air feed motorcomprising, in combination, a room thermostat, a combustion thermostat,a source of power, connections for energizing the fuel feed and air feedmotors when the temperature to which the room thermostat is subjectedfalls below a predetermined minimum and other connections controlled bythe combustion thermostat for de-energizing the fuel feed motor onlywhen the temperature of combustion rises above a predetermined maximumwhile the temperature at the room thermostat remains below the desiredminimum.

5. A control system comprising, in combination, a room thermostat, arelay controlled thereby, a fuel feed motor, an air feed motor, circuitconnections controlled by the relay for energizing the fuel feed motorand the air feed motor, a combustion thermostat and means controlled bythe combustion thermostat for preventing operation of the fuel feedmotor only when the temperature of combustion rises above apredetermined maximum.

6. A control system for an automatic stoker including an electric motorfor controlling fuel feed and a second electric motor for controllingthe supply of air comprising, in combination, a room thermostat, acombustion thermostat, a source of power, connections controlled by theroom thermostat for operating the fuel feed and air supply motors whenthe room temperature falls below a predetermined minimum, connectionscooperating with the combustion thermostat and fuel feed motor forpreventing operation thereof when the temperature of combustion risesabove a predetermined maximum while the room temperature remains belowthe predetermined minimum and other connections cooperating with thecombustion thermostat for operating both the fuel feed motor and airsupply motor when the temperature of combustion falls below apredetermined minimum while the room temperature is above itspredetermined minimum.

7. An automatic control system comprising in combination, a fuel feedmotor, an air feed motor, a relay in control of said motors, a roomthermostat for energizing the relay to operate the fuel feed and airfeed motors when the room temperature falls below a predeterminedminimum, a combustion thermostat, a circuit controlled thereby forpreventing operaton of the fuel feed motor only, rises above apredetermined maximum while the room temperature remains below itspredetermined minimum and other circuit connections between the relayand combustion thermostat for energizing the relay when the temperatureof combustion falls below a predetermined minimum to operate the fuelfeed motor and air supply motor when the room temperature is above itspredetermined minimum.

8. An automatic control system comprising, in combination, a roomthermostat, a source of power, a relay in circuit with the source ofpower and room thermostat, a switch operated by the relay, an air feedmotor, a fuel feed motor, a circuit for the air feed motor including thesource of power, relay operated switch, and air feed motor, a combustionthermostat, a switch operated thereby, and a circuit for the fuel feedmotor including the source of power, relay operated switch, combustionthermostat switch and fuel feed motor.

9. A control system comprising in combination, a source of power, arelay, a room thermostat, a combustion controlled low limit switch,parallel circuits for the relay controlled by the room therwhen thetemperature of combustion mostat and combustion controlled low limitswitch,

a fuel feed motor, an air feed motor, a switch mechanism operated toclosed circuit position when the relay is energized, a circuit for theair feed motor including the source of power and relay controlled switchmechanism, a combustion temperature high limit switch and a circuit forthe fuel feed motor including the source of power, the relay controlledswitch mechanism and combustion temperature high limit switch.

10. A control system for an automatic stoker including an air feed and afuel feed comprising, in combination, a thermostatic device located inthe space to be heated, a. furnace thermostat directly responsive to thetemperature of combustion, means under control of the thermostaticdevice for operating the air feed and fuel feed when the temperature ofthe space to be heated is below that desired, means under control of thefurnace thermostat for interrupting operation of the fuel feed when thetemperature of combustion rises above a predetermined maximum, and meansfor operating the fuel feed sufficiently often to prevent extinguishmentof the fire under low heat requirement conditions.

temperature to which said thermostat responds rises above apredetermined maximum.

14. A control system for a combustion system including a heater, a fuelfeed and an air feed, said control system comprising, means foroperating the fuel feed and air feed, a thermostat responsive to aheater condition, means under the control of said thermostat for onlydiscontinuing operation of the fuel feed and allowing continuedoperation of the air feed when the temperature to which said thermostatresponds rises above a predetermined maximum, and means for operatingthe fuel feed sufficiently often to prevent extinguishment of the firewhen the combustion system is operating under low heat requirementconditions.

15. A control system for a combustion system including a fuel feed andan air feed, said con trol system comprising, means for operating thefuel feed and air feed, a thermostat directly responsive to combustionconditions, and means controlled by said thermostat for interruptingoperation of the fuel feed and allowing continued operation of the airfeed when the temperature of combustion rises above a predeterminedmaxi- 11. A control system for an automatic stoker mum including anelectric motor for controlling fuel feed and a second electric motor forcontrolling the supply of air comprising, in combination, a roomthermostat, a combustion thermostat, a source of power, connectionscontrolled by the room thermostat for operating the fuel feed and airsupply motors when the room temperature falls below a predeterminedminimum, connections oo-operating with the combustion thermostat andfuel feed motor for preventing operation thereof when the temperature ofcombustion rises above a predetermined maximum while the roomtemperature remains below the predetermined minimum and means foroperating the fuel feed means sufliciently often to preventextinguishment of the fire unler low heat requirement conditions.

12. An automatic control system comprising in combination, a fuel feedmotor, an air feed motor, a relay in control of said motors, a roomthermostat for energizing the relay to operate the fuel feed and airfeed motors when the room temperature falls below a predeterminedminimum, a combustion thermostat, a circuit controlled thereby forpreventing operation of the fuel feed motor only, when the temperatureof combustion rises above a predetermined maximum while the roomtemperature remains below its predetermined minimum and means forenergizing the relay to operate the fuel feed motor and air supply motorsufiiciently often to prevent extinguishment of the fire under low heatrequirement conditions.

13. A control system for a combustion system including a heater, a fuelfeed and an air feed, said control system comprising, means foroperating the fuel feed and air feed, a thermostat responsive to aheater condition, and means under the control of said thermostat foronly discontinuing operation of the fuel feed and allowing continuedoperation of the air feed when the 16. A control system for a combustionsystem including a fuel feed and an air feed, said control systemcomprising, means for operating the fuel feed and air feed, a thermostatdirectly responsive to combustion conditions, means controlled by saidthermostat for interrupting operation of the fuel feed and allowingcontinued operation of the air feed when the temperature of combustionrises above a. predetermined maximum, and means for operating the fuelfeed sufficiently often to prevent extinguishment of the fire when thecombustion system is operating under low heat requirement conditions.

17. A system of the class described comprising, in combination, a fuelfeed, an air feed, a primary thermostatic control device, meanscontrolled thereby for operating the fuel feed and air feed, a secondarythermostatic control device responsive to a heater condition, and meansunder the control thereof for interrupting operation of the fuel feedand allowing continued operation of the air feed when the temperature towhich said secondary thermostatic control device responds rises above apredetermined maximum.

18. A system of the class described comprising, in combination, a fuelfeed, an air feed, a primary thermostatic control device, meanscontrolled thereby for operating the fuel feed and air feed, a secondarythermostatic control device responsive to a heater condition, and meansunder the control thereof for interrupting operation of the fuel feedand allowing continued operation of the air feed when the temperature towhich said second thermostat responds rises above a predeterminedmaximum and for operating the fuel feed sufiiciently often to preventextinguishment of the fire when operating under low heat requirementconditions.

THOMAS MCDONALD. CLIFFORD J. PAISLEY.

